1. Field of the Invention
This invention concerns room temperature-curable polyorganosiloxane compositions. More precisely, this invention concerns room temperature-curable polyorganosiloxane compositions which are characterized by the fact that the postcure surface is not easily soiled and the area near the substrate, with which the cured product is in contact, is not contaminated.
2. Description of the Prior Art
Conventionally, room temperature-curable polyorganosiloxane compositions, especially polyorganosiloxane compositions which form rubbery substances after curing at room temperature, have been widely used as electric insulating materials, mold making materials, gaskets, and sealants. However, dust is easily adhered or adsorbed when these room temperature-curable polyorganosiloxanes are used in the above-mentioned applications. In particular, when used as architectural sealants on building exteriors, liquid polyorganosiloxane slowly migrates from the cured silicone rubber onto the surrounding building wall surface which absorbs the stain and the building's appearance deteriorates. One method for overcoming these drawbacks is the addition to the composition of a surfactant such as a polyoxyalkylene compound or its copolymer with an organopolysiloxane (cf. Japan Kokai Patent No. Sho 56 [1981]-76453 and Japan Kokai Patent No. Sho 56[1981]-76452). In these methods, when a surfactant is added in an amount adequate for the prevention of soiling, the adhesiveness, an essential characteristic of an architectural sealant, is significantly impaired. Also, the weather resistance of polyether bonds is poor and when these materials are used outdoors and exposed to direct sunlight the soiling prevention effect is rapidly reduced.
The inventors earnestly pursued the present study in an attempt to overcome the drawbacks of conventionally known room temperature-curable polyorganosiloxane compositions that are easily soiled. This invention was achieved as a result.